This invention relates to the field of geological defect detection methods and devices, and more particularly to a novel and advantageous infrared thermographic sensing system and methodology using video cameras and infrared scanners to create both video and infrared images which are analyzed simultaneously with location information for detection of subterranean anomalies in geological areas.
Geological areas often contain subterranean anomalies such as erosion cavities, small caves, or voids (large open spaces, for example, above old sewers), abandoned or leaking utility pipes, pulverized or deteriorating ("punky") concrete, buried storage tanks or other large objects. If ignored, these anomalies may deteriorate and the ground surrounding them may crumble until the surface eventually collapses. At the very least, such cave-ins result in economic loss which could be avoided by early detection of the problem and subsequent remedial measures. If the defect results in a very large cave-in (sink-hole) or perhaps an extensive natural gas leak, there could also be loss of life. Prevention of these disasters invariably is less expensive than remedial measures.
Historically, utility companies and highway departments have attempted to locate problem sites by a variety of methods. Other than waiting for a cave-in to occur or for a leak to come to the surface, the following methods have also been used: physical inspection of surface areas for cracks, bulges, or depressions; sending personnel literally to crawl through sewers and take photographs of suspicious areas; "sounding" along the surface to detect differences in tone indicative of possible problem sites; boring out samples to detect variations in the subsoil; scanning the surface with metal detectors, penetrating tee ground with a probe to transmit and receive radar or infrared signals and thus detect variations in stratigraphic trends, or electrical contrasts; and testing with a falling weight deflectometer to detect variations in pavement surfaces. Miscellaneous inadequacies exist with each of the above defect detection methods.
Crawl-through teams face the risks of poisonous gasses, scalding, flooding or collapse of the sewer around them, yet from inside a sewer they are unable to detect many voids which may exist in the surrounding earth. Other invasive methods such as taking core samples or penetrating the surface with a radar probe are time-consuming and inaccurate and may increase the risk of a cave-in. Metal detectors may detect buried drums or tanks but of course cannot reveal the presence of voids or other non-metallic objects, such as abandoned gravesites or plastic pipes or drums. The ground-probing radar method may suffer from electronic interference, for example due to water lines, and requires a trained geophysicist to interpret the results. Leaking gas or water lines which have not yet washed away the surrounding soil will very likely be missed by conventional defect detection methods. All of the above methods are inefficient in terms of time and personnel required, as well as being inaccurate to varying degrees.
More recently, various methods of infrared thermography have been used to detect subsurface geological anomalies. In one method, referred to herein as the "hand-held" method, still images have been taken of the same general area using both an infrared scanner and a hand-held camera. The resultant infrared image, or thermogram, is analyzed for variations in relative temperature over the test area. The visual snapshot is later compared to the thermogram to attempt to locate a defect within the study area. For example, the image of a man seen standing in the snapshot will be noted on the thermogram by a different temperature "signature," or color. Likewise, as later explained, a geological anomaly will present its own unique thermographic signature.
The hand-held method of defect detection presents several problems. The infrared and visual images must be taken from a point well above the suspect geological surface area; this requires that two sets of personnel must be on hand, one to operate the equipment from, for example, a tower, roof-top or cherry-picker and another to work on the ground, marking comparison positions, etc. The two crews must communicate by hand-signals, walkie-talkies, or the like. This hand-held imaging method is time-consuming and inefficient because only a limited area can be imaged from a given position. Then the crews must pack up their equipment and reposition at another site for a different angle of the same area or to view another test area. These limitations made the method inadequate for evaluating very large geological areas, for example, long stretches of highway, sewer routes or airport runways.
A variation on the hand-held method is known, in which the infrared unit actually scans a test area as the unit is moved over the area by being mounted on a tripod on a truck or helicopter, for example. That method also requires comparison of thermograms with still photographs taken at various sites within the test area. In this method location markers may be manually applied to the test area, such as by setting flares to act as thermographic and visual markers or by painting footage markers along the entire section of pavement to be scanned, perhaps for miles.
In both of the above thermographic methods a great deal of time and manpower is required to perform even one test. Furthermore, because the thermogram and snapshots are not in goo registration with each other, much time is spent in comparative analysis of the infrared and visual images to detect the precise anomalie location within the viewed area. A location error of even ten or twenty feet can result in maintenance crews wasting inordinate amounts of time and money while attempting to locate the problem.